This invention relates to light sensors.
RFID (Radio Frequency Identification) refers to the use of an electronic device, generally called RFID tag, incorporated into a target (goods or life beings). This device is used to transmit information from the target to a reader using radio frequencies.
RFID tags typically consist of an RFID transmitter for modulating and demodulating a radio-frequency (RF) signal, an RFID antenna for receiving and transmitting the signal, and an integrated circuit for storing and processing information and other specialized functions.
RFID tags can be active, if they contain a power source which allows them to operate independently, or passive, if the power is induced from an external source, typically via the RFID reader itself.
RFID sensors are a particular variation of RFID tags. Typically RFID tags are used for identification purposes. By integrating sensors into the RFID tag, much more functionality becomes available.
In an application of an RFID sensor, the environmental conditions to which a particular product is exposed can be tracked during its lifetime in the supply chain, and then transmitted to an RFID reader. The use of integrated sensors allows the monitoring of environmental conditions to which a perishable product is exposed. With appropriate algorithms, this data can be translated into estimation of remaining lifetime.
In order for an RFID sensor to be economically viable, the price of the sensor must be significantly less than the price of the product to be monitored.
The cost of the global annual waste of perishable products totals approximately US$35 Billion. This includes food, drinks, flowers, pharmaceuticals, vaccines, blood, and chemicals. The cold chain represents the refrigerated and controlled supply chain of these products from production, transportation, and storage to the end-user. By smart tagging of perishable products, a great deal of waste can be avoided. RFID tags on the products and containers include sensors for a number of environmental parameters such as temperature, humidity, O2/CO2 concentration and pH.
The light dose is a very important parameter influencing the quality and lifetime of perishables (see for example, Nicola E. Fontana, Cultivation management on the farm influences postharvest quality and safety, International Conference on Quality Management of Fresh Cut Produce, 2007). A light sensor integrated into an RFID sensor monitors the light dose certain goods have received. This information must be stored until an external RFID readout occurs. In order to store the sensor readout, a memory is required. However the use of a memory has some disadvantages; for example a power supply is required to program or keep the data in the memory and furthermore the circuit is more complex, resulting in a more costly sensor.
Therefore, there is a need to develop a cheaper light sensor.